diff --git a/app/harness/checkpoint.py b/app/harness/checkpoint.py
index 5c57544..c0849d6 100644
--- a/app/harness/checkpoint.py
+++ b/app/harness/checkpoint.py
@@ -41,6 +41,7 @@ _STRUCTURAL_KEYS = (
     "diag_size",
     "val_size",
     "batch_correct_ratio",
+    "trainable_min_units",
 )
 
 _DECISION_KEYS = (
diff --git a/app/harness/config.py b/app/harness/config.py
index 9e05241..824735d 100644
--- a/app/harness/config.py
+++ b/app/harness/config.py
@@ -60,6 +60,7 @@ class RunConfig:
         batch_size: mini-batch 单批题目数。
         min_class_per_batch: 单批中每个任务类型至少保留的题目数（< batch_size）。
         eval_min_per_class: 验证池中每个任务类型至少保底的题目数。
+        trainable_min_units: 可训练性预检：每题型 diag+val 单元数下限，低于则剔除该题型。
         early_stop_patience: 全局 best 连续未提升的容忍轮数，达到即早停。
         test_size: held-out 测试池题目数。
         use_slow_momentum: 是否启用快慢双速进化中的慢速 momentum 更新。
@@ -114,6 +115,7 @@ class RunConfig:
     batch_size: int
     min_class_per_batch: int
     eval_min_per_class: int
+    trainable_min_units: int
     early_stop_patience: int
     test_size: int
     use_slow_momentum: bool
@@ -297,6 +299,8 @@ def _validate_minibatch(config: RunConfig) -> None:
         )
     if config.eval_min_per_class < 1:
         raise ValueError(f"eval_min_per_class 必须 >= 1，实际: {config.eval_min_per_class}")
+    if config.trainable_min_units < 1:
+        raise ValueError(f"trainable_min_units 必须 >= 1，实际: {config.trainable_min_units}")
     if config.pool_split_mode != "per_category":
         floor = config.eval_min_per_class * _VIDEO_MME_TASK_TYPE_COUNT
         if config.val_size < floor:
diff --git a/app/harness/runner.py b/app/harness/runner.py
index 97ddda9..ea6ebc1 100644
--- a/app/harness/runner.py
+++ b/app/harness/runner.py
@@ -18,7 +18,8 @@ import random
 import shutil
 import sqlite3
 import tempfile
-from dataclasses import dataclass, field
+from collections import Counter
+from dataclasses import dataclass, field, replace
 from pathlib import Path
 from typing import TYPE_CHECKING, Any
 
@@ -288,6 +289,52 @@ def _snapshot_current_skills(skills_dir: Path) -> dict[str, str]:
     return snapshot
 
 
+def _filter_untrainable_types(
+    pools: Pools,
+    task_types: list[str] | None,
+    eval_min_per_class: int,
+    trainable_min_units: int,
+) -> tuple[Pools, list[str] | None]:
+    """剔除不可训练题型（val<eval_min_per_class 或 非test单元<trainable_min_units）。
+
+    非test单元数 = 该题型 diag+val 题数（single 题 unit==题；等于 gate 阶梯该类候选数）。
+    test 池不过滤（继续报告全题型准确率）。在 gate 建立前调用，避免样本不足的
+    微型题型进入信息量阶梯导致门控崩溃。
+
+    参数:
+        pools: 冻结三池。
+        task_types: 显式题型子集（None 表示全部），过滤后按 keep 收窄。
+        eval_min_per_class: 验证池每类保底题数下限。
+        trainable_min_units: 每类可训练所需最小 diag+val 单元数。
+
+    返回:
+        过滤后的 (pools, task_types)：pools.diagnosis/validation 仅保留 keep 题型，
+        test 原样；task_types 收窄为 keep（原 None 时返回 sorted(keep)）。
+    """
+    diag_by_type = Counter(q.task_type for q in pools.diagnosis)
+    val_by_type = Counter(q.task_type for q in pools.validation)
+    keep: set[str] = set()
+    dropped: list[tuple[str, str]] = []
+    for tt in set(diag_by_type) | set(val_by_type):
+        n_val = val_by_type.get(tt, 0)
+        n_units = diag_by_type.get(tt, 0) + n_val
+        if n_val < eval_min_per_class:
+            dropped.append((tt, f"val={n_val}<{eval_min_per_class}"))
+        elif n_units < trainable_min_units:
+            dropped.append((tt, f"units={n_units}<{trainable_min_units}"))
+        else:
+            keep.add(tt)
+    for tt, why in sorted(dropped):
+        logger.warning("可训练性预检剔除题型 {}（{}）", tt, why)
+    new_pools = replace(
+        pools,
+        diagnosis=[q for q in pools.diagnosis if q.task_type in keep],
+        validation=[q for q in pools.validation if q.task_type in keep],
+    )
+    new_types = [t for t in task_types if t in keep] if task_types is not None else sorted(keep)
+    return new_pools, new_types
+
+
 def _should_early_stop(
     workspace_dir: Path,
     epoch: int,
@@ -790,8 +837,20 @@ class Runner:
         三级嵌套：epoch → batch(step) → per-skill。
         epoch 末 _slow_update_cycle 十步序。
         训练收尾 _deliver_best + _final_test_eval。
+
+        入口第一步做可训练性预检：剔除样本不足的微型题型（防 gate 阶梯崩溃），
+        过滤后的 pools 贯穿 batch/step/slow-update/final-eval 全部消费；filtered_task_types
+        透传到 gate 建立（不改 frozen RunConfig）。
         """
-        state, total_steps, plan, saved_batches = await self._setup_train_run(pools)
+        pools, filtered_task_types = _filter_untrainable_types(
+            pools,
+            list(self._config.task_types) if self._config.task_types is not None else None,
+            self._config.eval_min_per_class,
+            self._config.trainable_min_units,
+        )
+        state, total_steps, plan, saved_batches = await self._setup_train_run(
+            pools, filtered_task_types
+        )
         for epoch in range(plan["first_epoch"], self._config.epochs + 1):
             if epoch == plan["resume_epoch"]:
                 batches = [_batch_from_ids(pools, ids) for ids in saved_batches]
@@ -859,16 +918,22 @@ class Runner:
     # 训练初始化
     # -----------------------------------------------------------------------
 
-    async def _setup_train_run(self, pools: Pools) -> tuple[_TrainState, int, dict, list | None]:
+    async def _setup_train_run(
+        self, pools: Pools, filtered_task_types: list[str] | None
+    ) -> tuple[_TrainState, int, dict, list | None]:
         """据是否 --resume 准备训练起点。
 
+        参数:
+            pools: 已过可训练性预检的三池。
+            filtered_task_types: 预检后保留的题型（None 表示不限，由 gate 从 diag 推导）。
+
         返回:
             (state, total_steps, plan, saved_batches)。
         """
         ckpt = load_checkpoint(self._config.workspace_dir) if self._config.resume else None
         if self._config.resume and ckpt is None:
             raise RuntimeError("--resume 但 checkpoint.json 不存在，拒绝静默从头重训")
-        gate_pools, baseline_cache = self._init_gate_pools(pools)
+        gate_pools, baseline_cache = self._init_gate_pools(pools, filtered_task_types)
         if not ckpt:
             state = self._init_train_state(pools, gate_pools, baseline_cache)
             total_steps = _compute_total_steps(pools, state.correctness, self._config)
@@ -894,13 +959,16 @@ class Runner:
         )
         return state, ckpt["progress"]["total_steps"], plan, ckpt["epoch_batches"]
 
-    def _init_gate_pools(self, pools: Pools) -> tuple[GatePools, BaselineCache]:
+    def _init_gate_pools(
+        self, pools: Pools, filtered_task_types: list[str] | None
+    ) -> tuple[GatePools, BaselineCache]:
         """构建/加载 CE-Gate 信息量阶梯与基线缓存。
 
         副作用：设置 self._gate_questions_by_id（不进 checkpoint）。
 
         参数:
-            pools: 冻结三池。
+            pools: 冻结三池（已过可训练性预检）。
+            filtered_task_types: 预检保留的题型；None 时从 pools.diagnosis 推导。
 
         返回:
             (GatePools, BaselineCache)。
@@ -931,7 +999,12 @@ class Runner:
             )
         baseline_correctness = {r["question_id"]: r["prediction"] == r["answer"] for r in rows}
         logger.info("gate 阶梯基线对错覆盖 {} 题", len(baseline_correctness))
-        gate_task_types = sorted({q.task_type for q in pools.diagnosis})
+        # 预检保留的题型优先；None 时从（已过滤的）诊断池推导，二者一致
+        gate_task_types = (
+            sorted(filtered_task_types)
+            if filtered_task_types is not None
+            else sorted({q.task_type for q in pools.diagnosis})
+        )
         gate_pools = build_or_load_gate_pools(
             workspace_dir=self._config.workspace_dir,
             questions=questions,
diff --git a/config/default.yaml b/config/default.yaml
index 63c5e0a..0048741 100644
--- a/config/default.yaml
+++ b/config/default.yaml
@@ -67,6 +67,7 @@ harness:
   batch_correct_ratio: 0.5
   momentum_samples: 20
   eval_min_per_class: 2
+  trainable_min_units: 8
   early_stop_patience: 8
   use_slow_momentum: true
   # 池构建策略
diff --git a/config/train_action_recognition.yaml b/config/train_action_recognition.yaml
index 9aa68db..a80a3db 100644
--- a/config/train_action_recognition.yaml
+++ b/config/train_action_recognition.yaml
@@ -48,6 +48,7 @@ harness:
   batch_correct_ratio: 0.5
   momentum_samples: 20
   eval_min_per_class: 2
+  trainable_min_units: 8
   early_stop_patience: 4
   test_size: 63
   diag_size: 20
diff --git a/tests/unit/test_harness_checkpoint.py b/tests/unit/test_harness_checkpoint.py
index 1d5d40e..e1fc36f 100644
--- a/tests/unit/test_harness_checkpoint.py
+++ b/tests/unit/test_harness_checkpoint.py
@@ -157,6 +157,7 @@ class _FakeConfig:
     diag_size: int = 30
     val_size: int = 50
     batch_correct_ratio: float = 0.5
+    trainable_min_units: int = 8
     edit_budget_start: int = 6
     edit_budget_end: int = 3
     early_stop_patience: int = 3
@@ -289,6 +290,7 @@ class TestFingerprintStructuralVsDecision:
             "diag_size",
             "val_size",
             "batch_correct_ratio",
+            "trainable_min_units",
         }
         decision = {
             "edit_budget_start",
diff --git a/tests/unit/test_harness_config.py b/tests/unit/test_harness_config.py
index b744b51..7a689bd 100644
--- a/tests/unit/test_harness_config.py
+++ b/tests/unit/test_harness_config.py
@@ -40,6 +40,7 @@ def _valid_kwargs() -> dict:
         "batch_size": 15,
         "min_class_per_batch": 2,
         "eval_min_per_class": 2,
+        "trainable_min_units": 8,
         "early_stop_patience": 8,
         "test_size": 60,
         "use_slow_momentum": True,
diff --git a/tests/unit/test_harness_pools.py b/tests/unit/test_harness_pools.py
index 2cc1b75..48cc3d6 100644
--- a/tests/unit/test_harness_pools.py
+++ b/tests/unit/test_harness_pools.py
@@ -317,6 +317,7 @@ class TestBuildOrLoadPoolsFrozen:
             batch_size=15,
             min_class_per_batch=2,
             eval_min_per_class=2,
+            trainable_min_units=8,
             early_stop_patience=4,
             test_size=10,
             use_slow_momentum=True,
@@ -870,6 +871,7 @@ class TestRunHoldoutEvalConfig:
             batch_size=15,
             min_class_per_batch=2,
             eval_min_per_class=2,
+            trainable_min_units=8,
             early_stop_patience=4,
             test_size=30,
             use_slow_momentum=True,
@@ -920,6 +922,7 @@ class TestRunHoldoutEvalConfig:
             batch_size=15,
             min_class_per_batch=2,
             eval_min_per_class=2,
+            trainable_min_units=8,
             early_stop_patience=4,
             test_size=30,
             use_slow_momentum=True,
diff --git a/tests/unit/test_harness_runner.py b/tests/unit/test_harness_runner.py
index 619a689..f328f04 100644
--- a/tests/unit/test_harness_runner.py
+++ b/tests/unit/test_harness_runner.py
@@ -20,6 +20,7 @@ from app.harness.runner import (
     _build_comparison_pairs,
     _compute_total_steps,
     _fallback_summary,
+    _filter_untrainable_types,
     _format_applied_edits,
     _guard_infra_failures,
     _outcome_to_quadrant_pairs,
@@ -401,6 +402,58 @@ class TestShouldEarlyStop:
         assert state.epochs_since_best_improved == 2
 
 
+class TestFilterUntrainableTypes:
+    """_filter_untrainable_types 可训练性预检纯函数。"""
+
+    def test_untrainable_types_filtered_before_gate(self) -> None:
+        """val<eval_min_per_class 或 非test单元<trainable_min_units 的题型被剔除。"""
+        # 题型 A：diag=5 + val=5 → units=10、val=5，可训
+        diag = [_FakeQuestion(question_id=f"A-d{i}", task_type="A") for i in range(5)]
+        val = [_FakeQuestion(question_id=f"A-v{i}", task_type="A") for i in range(5)]
+        # 题型 B：val=0（<eval_min_per_class）不可训
+        diag += [_FakeQuestion(question_id=f"B-d{i}", task_type="B") for i in range(2)]
+        pools = _FakePools(diagnosis=diag, validation=val, test=[])
+
+        new_pools, new_types = _filter_untrainable_types(
+            pools,
+            task_types=["A", "B"],
+            eval_min_per_class=2,
+            trainable_min_units=8,
+        )
+
+        assert {q.task_type for q in new_pools.diagnosis} == {"A"}
+        assert {q.task_type for q in new_pools.validation} == {"A"}
+        assert new_types == ["A"]
+
+    def test_units_below_threshold_filtered(self) -> None:
+        """val 达标但 diag+val 单元数 < trainable_min_units 的题型被剔除。"""
+        # 题型 C：val=2（>=2）但 units=2+0=... 补 diag 使总数不足
+        val = [_FakeQuestion(question_id=f"C-v{i}", task_type="C") for i in range(2)]
+        diag = [_FakeQuestion(question_id="C-d0", task_type="C")]  # units=3 < 8
+        pools = _FakePools(diagnosis=diag, validation=val, test=[])
+
+        new_pools, new_types = _filter_untrainable_types(
+            pools, task_types=None, eval_min_per_class=2, trainable_min_units=8
+        )
+
+        assert new_pools.diagnosis == []
+        assert new_pools.validation == []
+        assert new_types == []
+
+    def test_test_pool_untouched(self) -> None:
+        """test 池不参与过滤（继续报告全题型准确率）。"""
+        val = [_FakeQuestion(question_id=f"A-v{i}", task_type="A") for i in range(8)]
+        diag = [_FakeQuestion(question_id=f"A-d{i}", task_type="A") for i in range(8)]
+        test = [_FakeQuestion(question_id="B-t0", task_type="B")]
+        pools = _FakePools(diagnosis=diag, validation=val, test=test)
+
+        new_pools, _ = _filter_untrainable_types(
+            pools, task_types=None, eval_min_per_class=2, trainable_min_units=8
+        )
+
+        assert new_pools.test == test
+
+
 # =========================================================================
 # 13c: Probation 数据结构测试
 # =========================================================================
@@ -690,6 +743,7 @@ class TestRunnerFactoryInjection:
             "batch_size": 5,
             "min_class_per_batch": 2,
             "eval_min_per_class": 2,
+            "trainable_min_units": 8,
             "early_stop_patience": 3,
             "test_size": 10,
             "use_slow_momentum": False,
diff --git a/tests/unit/test_runner_diag_tree_inject.py b/tests/unit/test_runner_diag_tree_inject.py
index 404b649..43dbab3 100644
--- a/tests/unit/test_runner_diag_tree_inject.py
+++ b/tests/unit/test_runner_diag_tree_inject.py
@@ -54,6 +54,7 @@ def _base_config(workspace_dir: Path, store_dir: Path) -> RunConfig:
         batch_size=5,
         min_class_per_batch=2,
         eval_min_per_class=2,
+        trainable_min_units=8,
         early_stop_patience=3,
         test_size=10,
         use_slow_momentum=False,